Japanese Patent No. 4068268 discloses an example of a known method of charging a lead storage battery.
An object of the method of charging a lead storage battery in Japanese Patent No. 4068268 is to solve a problem, “in a quick charge method using a relatively large constant current of at least 1.0 C, a battery voltage reaches at least a gas generating voltage and generates oxygen gas and hydrogen gas before charging of a sufficient amount, leading to a reduction in charging efficiency and degradation of life characteristics”. The charging method is pulse charging in which a lead storage battery is charged by a constant current of at least 1.0 C for a predetermined energization time T1, and then the charging of the lead storage battery is stopped for a predetermined stop time T2. The energization time T1 ranges from 0.005 seconds to less than 0.1 seconds, and the stop time T2 is set below 0.1 seconds. The energization time T1 and the stop time T2 are set so as to satisfy the relationship of T1≦T2≦3T1. According to “Pulse Charging Characteristics of Control-valve Lead Battery for Electric Vehicle” in “1999 IEEJ National Convention Journal 4” issued on Feb. 10, 1999 by IEEJ National Convention Committee, the pulse is disclosed as a perfect square wave.
According to this method, when a battery is charged to a certain degree, polarization components rapidly increase a voltage to at least a gas generation voltage and gas is generated from electrodes during energization, reducing charging efficiency. Such an increase in voltage by the polarization components can be suppressed by shortening the energization time T1 and the stop time T2, enabling efficient charging.
However, the known method of charging a lead storage battery does not disclose a charging apparatus, that is, a specific method of generating a pulse specified by the energization time T1 and the stop time T2 with a constant current of at least 1.0 C. Specifically, for example, assuming that 1 C of a lead storage battery is an ordinary current of 30 A, a charging apparatus that generates a pulse with a perfect square wave applies a current of at least 30 A (at least 1.0 C), e.g., 50 A for a time period of at least 0.005 seconds to less than 0.1 seconds and stops the current application for less than 0.1 seconds, resulting in a complicated circuit configuration. Thus, it is actually difficult to achieve an inexpensive apparatus, leading to extremely high cost.
Moreover, for various kinds (ratings) of lead storage batteries with different rated currents, a simple adjustment to a charging current has been demanded.